1. Field of the Invention
This invention relates to a titanium trichloride useful as a Ziegler-type catalyst component. The invention further relates to the method of producing titanium trichloride catalyst component and a method for polymerizing alpha-olefins such as propylene to highly stereoregular polyolefins in the presence of the titanium trichloride catalyst component and a cocatalyst such as an organoaluminum compound. More particularly, the invention relates to a highly active, highly crystalline shear resistant titanium trichloride which has been prepolymerized with a small amount of alpha-olefin.
2. Discussion of the Prior Art
Pretreatment of Ziegler-type catalysts with propylene is known in the art. The pretreatment is generally performed in order to stabilize the catalyst. For example, in British Pat. No. 1,300,734 (published Dec. 20, 1972) of Shell International Research Maatschappij N.V., it is taught that by contacting a Ziegler-type catalyst comprising a titanium halide and an organoaluminum compound with a small amount of an alpha-olefin a stabilized catalyst is obtained. By "stabilization", the patent teaches that reduction of catalytic activity during polymerization reaction does not occur such that the overall activity is maintained at a high level.
In accordance with British Pat. No. 1,384,603 of Shell International Research Maatschappij N.V., there is disclosed a titanium halide aluminum trialkyl polymerization catalyst which is stabilized against deteriorating during the polymerization reaction by prepolymerizing the catalyst at a temperature below 62.degree. C. prior to its being employed in the conventional polymerization reaction.
In the British Pat. No. 1,408,611 (published Oct. 1, 1975) of Shell International Research Maatschappij N.V. there is disclosed the preparation of a titanium trichloride catalyst component which involves reducing titanium tetrachloride to a beta-type titanium trichloride, activating the titanium trichloride to a gamma titanium trichloride and thereafter contacting the same with propene in order to form a prepolymerized catalyst component.
In U.S. Pat. No. 3,404,096 of Lamborn, issued Oct. 1, 1968, there is disclosed a method of pretreating Ziegler-type catalysts with ethylene so as to form a curdy catalyst component which is useful for obtaining friable fine catalyst particles.
In U.S. Pat. No. 3,689,597 of Mahlman, issued Sept. 5, 1972, there is disclosed a method of obtaining fine polypropylene particles by polymerizing propylene in the presence of a titanium trichloride catalyst which has been pretreated with alpha-olefins.
Several methods describing the activation of titanium trichloride obtained by low temperature reduction of titanium tetrachloride with an organoaluminum compound are described in the published patent literature. The activation is generally accomplished by contacting the reduction product of titanium tetrachloride with complexing agents and with various halogenated compounds to obtain a purple titanium trichloride which is useful as a co-catalyst with an organo-metal compound for the polymerization of alpha-olefins.
More particularly, in Japanese Patent Application (OPI) No. 34478/1972, published on Nov. 21, 1972 and corresponding to British Pat. No. 1,391,068 there is described a process which comprises treating the reduced solids obtained by low temperature reduction of titanium tetrachloride with an organoaluminum compound with a complexing agent, e.g., an ether, and titanium tetrachloride.
In Japanese Patent Application (OPI) No. 112289/1975, published Sept. 3, 1975, there is described a process wherein the titanium trichloride-containing reduced solids product obtained from the low temperature reduction of titanium tetrachloride in the presence of an organoaluminum compound is treated with a complexing agent, e.g., ethers, and then the resulting brown TiCl.sub.3 -containing catalyst is treated with carbon tetrachloride.
Additionally, in Japanese Patent Application (OPI) No. 143790/1975, published Nov. 19, 1975, a method is described comprising treating the reduced solids product with a mixture of a complexing agent and carbon tetrachloride.
In Japanese Patent Application (OPI) No. 149897/1976, published Dec. 23, 1976 and corresponding to British Pat. No. 1,484,086, there is described a process in which brown titanium trichloride obtained from the reduction of titanium tetrachloride in the presence of an organoaluminum halide and at low temperatures is subjected to heat treatment in the presence of a halogenated aliphatic or aromatic hydrocarbon in order to produce a violet titanium trichloride. It is further disclosed that the brown titanium trichloride obtained from the reduction step may be treated with a complexing agent, including ethers, prior to heat treatment.
In Japanese Patent Application (OPI) No. 227/1977, published Jan. 5, 1977, there is described a process which comprises heat-treating the reduced solid obtained from the low temperature reduction of titanium tetrachloride with an organoaluminum compound, treating the reduced solid with a complexing agent and then treating the resulting solids with an alkylaluminum dihalide or titanium tetrachloride.
Furthermore, in U.S. Pat. No. 3,825,524 there is described a process for the production of titanium trichloride catalyst having a high activity which includes contacting a crude titanium trichloride composition, obtained by reducing titanium tetrachloride with an organoaluminum chloride, with a mixed solvent system composed of (i) a main solvent of aliphatic or aromatic hydrocarbons, aromatic chlorinated hydrocarbons or trichloroethylene, and (ii) an auxilliary solvent, including ethers. The mixed solvent system is employed for the purpose of extracting undesirable components from the reduction product.
In co-pending U.S. Application Ser. Nos. 774,964, 774,946 and 774,947 there are disclosed processes for the production of titanium trichloride catalyst complexes useful for the polymerization of alpha-olefins in the presence of a co-catalyst such as an organo-metal compound. The process comprises reducing titanium tetrachloride with an organoaluminum halide compound at low temperature and thereafter treating at elevated temperatures the resulting reduced solid product with a chlorinated saturated hydrocarbon and in the further presence of a complexing agent such as an ether.
In Japanese Patent Application Publication No. Sho. 52-142691, of Chisso Corp., published Nov. 28, 1977, there is described a method of producing a titanium halide catalyst component wherein a small amount of propylene is present during the preparation of the titanium trichloride obtained during the reduction of titanium tetrachloride with an organoaluminum compound and therafter treating the obtained reduced solid with a Lewis acid and/or a complexing agent.
It is well known that during the formation of polyolefin particles obtained in the presence of transition metal halide catalysts, such as titanium halides, the polymer particles are essentially replicates of the catalyst particles. It is further known that during the activation of the titanium halides obtained from the low temperature reduction of titanium tetrachloride that the transition metal halide particles are friable, i.e., they will shear into smaller particles, i.e., fines. Therefore, it is highly desirable to obtain transition metal halide catalyst components which are essentially non-friable during activation and when subjected to mechanical shearing forces which may occur either during activation and polymerization.